This invention relates to primary electrochemical cells. More particularly, it is concerned with primary electrochemical cells having an oxidizable active anode material, a cathode current collector, and an electrolytic solution comprising a reducible liquid cathode material and an electrolyte solute dissolved therein.
A particularly effective class of primary electrochemical cells which employs soluble or liquid cathode materials, as opposed to the more conventional solid cathode cells, has undergone rapid development in recent years. In these cells, the active cathode material is usually a fluid solvent for an electrolyte solute which provides conductivity. The active anode of these cells is usually lithium or other highly electropositive metal. During discharge, the solvent is electrochemically reduced on a cathode current collector to yield ions, e.g. halide ions, which react with positive metal ions from the anode to form insoluble metal salts, e.g. metal halides. The cathde current collector does not take part in the reaction itself, but simply provides a support on which the reaction can occur, supplying electrons given up during the oxidation of the anode material.
A wide variety of materials have been employed to make up the cathode current collector or to provide a catalytically active surface thereof. An improved cathode current collector and methods of making it are described in U.S. Pat. No. 4,219,443 to Keith A. Klinedinst and Francis G. Murphy. This patent describes a cathode current collector having a surface layer of a finely divided catalyst for reducing the liquid cathode consisting of gold, platinum, or carbon black. U.S. Pat. No. 4,272,593 to Keith A. Klinedinst describes a cell having a cathode current collector including a catalyst which is a composite of carbon and platinum. This cathode current collector provides many of the advantages of a cathode current collector employing platinum at lower cost. However, the cost of platinum is such that electrochemical cells employing these cathode current collectors are uneconomical for many applications.